Ink ejectors or “jet stacks” are typically found in inkjet printers and enable controlled deposition of ink on a medium (e.g., paper) upon which printing is desired. Jet stacks are typically provided by a series of brazed steel plates, which include one or more manifolds to route ink received from ink reservoirs to an array of nozzles from which ink is dispensed. Jet stacks may also include actuators, for example, piezoelectric transducers connected to a power circuit, such that the actuators are selectively excitable. When excited, the actuators deflect, motivating a volume of ink to proceed through the nozzles and onto the medium. In this way, the deposition of the ink may be electrically controlled via the selective excitation of the actuators.
As higher resolution printing is desired, the density of actuators in the jet stacks increases, generally requiring smaller actuators. With piezoelectric transducers, however, reducing the size and increasing the number of transducers can lead to a variety of design and power challenges. For example, thinner, smaller piezoelectric transducers can be fragile and expensive to manufacture. Further, cost-effective electrical interconnects for such arrays of piezoelectric transducers can limit the practical density of the actuators.
Electrostatic actuators have been proposed to avoid such challenges. With electrostatic actuators, micro-electromechanical system (MEMS) technology can be employed, e.g., using microelectronics techniques such as deposition, lithography, etching, etc., to achieve gains in the scalability of the actuator arrays. Further, such electrostatic actuators can include a thin diaphragm bonded to a substrate, with the thin diaphragm flexing by application of electrostatic force, thereby providing the selectable motivation of the ink through the nozzles.
Implementation of such electrostatic actuators, however, presents other, unique challenges. For example, to fabricate the thin diaphragms, metal (or another material) is often rolled and/or etched to arrive at a desired thickness. However, in combined etching and rolling processes, rolling the thin layer can introduce grain defects in the material, which can reveal themselves during the etching process as pin holes. Furthermore, such etching processes are often capital intensive and require large volumes to justify the cost. Also, such etching processes may result in loose tolerances.
On the other hand, when the diaphragm is formed simply by rolling, the surface of the diaphragm generally conforms to the roller surface, and thus any defects in the surface of the rollers are exhibited in the material layer. Thus, the diaphragm, when produced by rolling operations, often requires secondary polishing processes to arrive at a desired smoothness. Further, the defects in the grain boundaries may be present in such non-etching fabrication processes as well. Moreover, with either technique, the resultant thin (e.g., 15-20 μm) diaphragm can be fragile, which may reduce yield productivity.
What is needed then is an improved electrostatic actuator and method for manufacturing such an actuator.